1. Field of the Invention
The present invention relates to a heat sink fan for cooling a micro processing unit (MPU) or other electrical component and a method for manufacturing a heat sink that is used for the heat sink fan.
2. Description of the Prior Art
A heat sink fan that is attached to an MPU or other heat generating electrical component usually includes a heat sink having a plurality of heat radiating fins that are placed on a MPU and extend radially from the central portion. The heat sink fan also includes a fan motor unit that has an axial flow fan with an impeller, which is surrounded by the heat radiating fins and is disposed at the central portion of the heat sink and at the inner side of the heat radiating fins. The heat radiating fins of the heat sink are cooled by air flow supplied by the axial flow fan.
One of structures for attaching the fan motor unit to the heat sink is disclosed in U.S. Pat. No. 6,419,007, for example. In this structure, a fan motor unit having a housing made of a synthetic resin is disposed above the heat sink, and four arm portions are formed at the periphery portion of the housing. Each of the arm portions extends from the housing to a base plate that is provided at the lower end of the heat sink so as to cover the outer side of the heat sink. A engaging portion is formed at the tip of the arm portion, and the engaging portion is engaged with an engaged portion formed on the base plate of the heat sink.
Another structure is disclosed in U.S. Pat. No. 5,484,013. In this structure, a housing of a fan motor unit is provided with a protrusion connecting integral to the housing and an arm portion connecting integral to the periphery of the housing. A pawl portion is provided at the tip of the arm portion. On the other hand, the heat sink is provided with a recess for receiving the protrusion of the housing and a flange portion for receiving the pawl portion of the housing. The protrusion of the housing is engaged with the recess of the heat sink, while the pawl portion of the housing is engaged with the flange portion of the heat sink, so that the fan motor unit is attached to the heat sink.
Recently, the amount of heat generated by an MPU has been increasing along with increase of processing speed and downsizing or larger scale of integration of the MPU. Therefore, the heat sink fan for cooling the MPU is required to be capable of supplying more cooling air to the heat sink so as to increase cooling efficiency.
However, if a rotation speed of the axial flow fan is increased so as to enhance the cooling efficiency for satisfying the above-mentioned requirement, the following problem may happen. Namely, the above-mentioned structure in which four arm portions extend from the housing to the substrate provided at the lower end of the heat sink has a disadvantage that when the air flow supplied by the axial flow fan flows along the heat radiating fins and is dissipated outside the heat sink, the arm portions disposed at the outer side of the heat radiating fins may interrupt the air flow. As a result, the air flow cannot be dissipated sufficiently into the outside of the heat sink, so that the cooling efficiency of the heat sink may be deteriorated. If members such as the arm portions exist more at the outer side of the heat radiating fins, or if the area where the members exist is larger, the air flow is interrupted more so that the cooling efficiency of the heat sink is deteriorated more. Therefore, it is desirable that there are as little members as possible at the outer side of the heat radiating fins.
In addition, if the arm portions of the housing are extended toward the lower end of the heat sink, a length of the arm portions becomes longer. As a result, the arm portions become easy to generate a distortion such as warping at the tip of the arm portion when housing is formed by resin molding. Consequently, it becomes difficult to finish precisely an engaging portion such as the pawl portion at the tip of the arm portion. In this case, it becomes difficult to attach the fan motor unit to the heat sink properly.
Moreover, the heat sink fan is also required to be inexpensive. Therefore, it is necessary to provide the heat sink fan with a simple structure that enables the fan motor unit to be attached to the heat sink easily and securely.